Method and apparatus for uniformly tensioning an advancing strand



Apnl 29, 1952 c. o. HAASE 2,594,427

METHOD AND APPARATUS FOR UNIFORMLY TENSIONING AN ADVANCING STRAND Filed May 22, 1947 F/G./ l l l/se FULL REEL EMPTY REEL A TORQUE MOTOR RPM.

FIG. 2

lNl EN TOR C. 0. HAASE ATTORNEY Patented Apr. 29, 1952 METHOD AND APPARATUS FOR UNIFORMLY TENSIONIN G AN ADVANCING STRAND Carl 0. Haase, Baltimore, Md., asslgnor to Western Electric Company, Incorporated, New York, N. Y., a, corporation of New York Application May 22, 1947, Serial No. 749,744

9 Claims.

This invention relates to methods of and apparatus for uniformly tensioning an advancing strand, and more particularly to methods of and apparatus for maintaining constant tension on a wire during the takeup operation of a wire drawing machine.

In the operation of modern high speed wire drawing machines used in the manufacture f fine wire, the wire emerging from the wire drawing machine is usually Wound on a suitable reel for further processing operations. This operation is generally referred to as the takeup operation and presents a peculiar problem in that while the Wire to be wound on the takeup reel is emerging from the wire drawing machine at a constant rate of speed, the winding diameter of the takeup reel is constantly increasing tending to increase the linear speed of the wire which results in an increased tension on the wire.

However, as constant tension must be maintained on the wire emerging from the wire drawing machine during the takeup operation, it has been the practice in the past in some instances to operate the takeup reel motor slightly above and slightly below the speed required to takeup the wire emerging from the machine and to control the torque of the motor between two selected points of operation by the actual tension being exerted on the wire. This type of operation places a decreased tension on the wire for a short interval and then an increased tension on the wire for a short interval, which alternating procedure is carried out during the entire takeup operation from an empty reel to a full reel. Obviously, when fine wire is involved, this principle of maintaining an average predetermined tension on the wire is objectionable because each changeover from low tension to high tension produces alternately loosely wound and tightly Wound layers on the reel. The tight convolutions pull down into the loosely wound sections, producing a reel of wire from which it is very difiicult to unwind the wire, thereby rendering the reel of wire unfit for use with high speed insulating machines, or the like.

An object of the invention is to provide new and improved methods of and apparatus for uniformly tensioning an advancing strand.

A further object of the present invention is to provide new and improved methods of and apparatus for maintaining a constant tension on a wire during the takeup operation of a wire drawing machine.

In accordance with one device embodying features of the invention, a plurality of pulleys are arranged to form an adjustable loop in the wire being advanced from a constant speed wire drawing machine to a variable speed takeup reel. The pulley forming the bottom or the loop is supported only by the wire and is free to travel up or down as the loop contracts or enlarges and is weighted to produce a desired tension on the wire. Means operable by the weighted pulley upon contraction or expansion of the adjustable loop alternately decreases and increases the torque and consequently the speed of the takeup reel motor in accordancewith the linear speed differential existing in the wire at the machine and the takeup reel.

The torque of the takeup reel motor is varied between selected limits, in accordance with the present method, by causing the weighted pulley to vary the input voltage to the motor, thereby causing the motor to operate on either of two preselected speed-torque curves. When the motor is operating on the lower speed-torque curve, the torque developed thereby is overcome by the weight carried by the pulley thereby reducing the speed of the motor so that the takeup speed of the wire is less than its supply speed. This operating condition allows the adjustable loop to enlarge to a predetermined size upon the happening of which the weighted pulley causes an increased potential to be supplied to the motor. The motor now operates on a higher speed-torque curve, where the torque of the motor overcomes the weight carried by the pulley, and the takeup speed of the wire is greater than its supply speed. This operation is alternately repeated until the takeup operation on the wire is completed.

A complete understanding of the invention will be had from the following detailed description of one embodiment thereof, when read in conjunction with the appended drawing, in which:

Fig. 1 shows diagrammatically a wire drawing apparatus and its takeup reel motor together with an electrical control circuit for the takeup reel motor, and

Fig. 2 shows diagrammatically the various speed-torque curves of the takeup reel motor obtainable upon the application of various input potentials to the motor.

Referring to Fig. 1 of the drawing, a reel [0 contains a supply of relatively coarse wire II, which is withdrawn therefrom and passed through a suitably mounted bell-shaped guide [2. The guide l2 directs the wire H to the first idler pulley of a bank of pulleys 13 forming part of a wire drawing apparatus, indicated generally at I4. The wire I I passes around the first pulley I3 through the first wire drawing die provided in a |3|3 and the capstan l6 until the wire has passed through each die of the die block l5 and is engaged by the last step of the capstan l5 When the motor 26 is energized, ina manner hereinafter to be described, the capstan|6 of, the wire drawing machine l4 serves to draw the wire. through each die in the die block l5, and the dies substantially reduce the diameter of the wire II to produce a relatively fine'wire indicated by the numeral 2 I. The wire 2| after passing several times around the last step of the capstan H5 is directed to aguide pulley 22 suitably mounted on a support indicated generally at 23.

The wire 2| passes around the pulley 22 and under a pulley 24 supported only by the Wire 2| and slidably positioned in agroove 25 provided in the support 23 and then to a pulley 26 rotatably mounted on the end of an arm 2'] pivotally mounted on the support 23. The arm 21 is resiliently supported in a substantially horizontal position by means of a spring 28. The wire. 2| passes over the pulley 26 andis engaged by asuitable traversing mechanism which serves tov distribute the wire 2| evenly across the winding surface of a takeup reel 3| mounted on a shaft 32, and driven by an induction motor 33.

The arrangement of the pulleys 22, 24 and 26 (Fig. 1) serves to form an adjustable loop in the wire 2| as. it advances from the final step of the capstan l6 to the-takeup reel 3|. The wire 2| is being delivered by the capstan It to the adjustable loop formed by these pulleys at. a constant rate of speed. Due to the fact that the windin diameter of the takeup reel 3| is constantly increasing as the takeup operation of the Wire 2| proceeds from an empty reel to a full reel, the linear speed of the wire 2| at the reel will, after a few layers of wire are wound on the reel, exceed, the linear speed or" the wire 2| as it leaves the capstan l6. The adjustable loop formed. by the pulleys 22, 24 and 26 permits the takeup reel 3| to alternately take up the wire 2| at a rate faster than it is being delivered by the capstan l6 and at a rate lower than it is beingdelivered by the capstan. The loop is, alternately contracted and, expanded to such an extent that the movable pulley 24 supported by theloop and riding in the groove 25 actuates suitable control mechanism to effect a change in the input potential applied to the motor 33 in a manner hereinafter to be described.

A weight 34 (Fig. l) restson the pulley 24 for the purpose of exerting a predetermined tension on the'wire 2| between the capstan I6 and the takeup reel 3|, regardless of the position of the pulley 24 in the groove 25. The spring 28 is arranged to hold the arm 21 in a normally horizontal position and is so designed that the arm Will remain in that position when the adjustable loop is tensioned by the weight 34 positioned on the pulley 24. The purpose of the spring 28 is to cushion the slight tension variations which. occur in the wire 2| due to the winding of the wire on the takeup reel 3| from layer to layer. A pair of spaced arms 35 and 36 are mounted pivotally on the support 23 so that one end of each of the arms extends into the path of travel of the'movable pulley 24. Each of the arms 35 and 36 has the opposite end thereof pivotall secured to the end of a trip arm 31, which is provided with an upper ear 40 and a lower ear 4|. A sensitive toggle switch 42 is mounted on the support 23 so that theend of its operating arm 43 is positioned between the ears 4D and 4| provided on the arm 31.

The trip arm 3'1 is raised and lowered alternately by the pulley 24 as the wire loop is contracted and expanded, thereby actuating the arm 43 of the switch 42, so that it alternately bridges apair'of upper contacts 44 and 45 and a pair of lower contacts 46 and 41. The contacts 44 and 46 are connected together and to a suitable electric controller indicated generally at 56 by means of a conductor 5|. The conductor 5| is connected to one. side of a suitable potential supply controlled by the apparatus included in the controller 53.

The contact 45 of the switch 42 is connected to one terminal of a coil 52, and the contact 41 is connected to one terminal of a coil 53 of a threepole, double throw magnetic contactor indicated generally by the numeral 54. The opposite terminals of the coils 52 and 53 are connectedtogether and to the control apparatus 53 by means of a conductor 55. The conductor 55 is connected to the opposite side of the potential supply to which the contacts 42 and 46 of the switch 42 are connected by the conductor 5|. Therefore, when the contacts 44 and 45 or the contacts 46 and 41 of the switch are bridged by the arm 43,

., the corresponding coil 52 or 53 of the contactor 54 is connected across a suitable potential supply eminating from the controller 53.

A three-phase potential supplied from a suitable source (not shown) is directed to the controller 5|] by a. three-pole switch 56. This threephase potential is directed by the controller 56 to the constant speed wire drawing motor 23 and to the takeup reel motor 33 through a Y-connected autotransformer 51 and suitable contacts provided on the contactor 54. The control apparatus 5|] may be of the type disclosed in C. O. Haase Patent 2,266,861, issued December 23, 1941, or may be of any other suitable type which will cause the motors 20 and 33 to operate in the manner hereinafter to be described.

Amagnetic clutch 66 is provided on the shaft 32, which when energized serves to connect the motor 23 directly to the shaft 32 by means of a pulley 6| provided on the shaft 32, a pulley 62 pro-- vided on the shaft and a driving element 63 engaged by the pulleys. The purpose of the magnetic clutch 60 is to connect the takeup reel 3| directly to the motor 2|] during the starting period of the wire drawing apparatus I4 so that the takeup reel 3| will have the same rate of acceleration as the wire drawing machine l4. After the wire drawing apparatus is brought up to speed by the motor 26, the control apparatus 50. serves to deenergize the magnetic clutch 50, whereupon the variable speed motor 33 is energized and takes over the operation of the takeup reel.3|.

The motor 33- is preferably a wound rotor, slipring type of induction motor having suitable resistances and reactances connected in the primary and secondary circuits thereof in such proportions that various input voltages will develop speed-torque curves substantially parallel to each other throughout the. selected speed range of the motor 33 from an empty reel to a full reel, as

winding diameter of the reelv is constantly increasing, therefore, a constantly decreasing motor torque is required. Under theoretically perfect operating conditions, if the motor 33 were operated on curve A, constant tension would be maintained on the wire 2| throughout the tak-eup operation of the wire from an empty reel to a full reel. But since perfect operating conditions cannot be obtained, due to variable factors such as friction, windage and line voltage, it is necessary to operate the motor alternately on a speed-torque curve B, which is obtained by applying a slightly increased input potential to the motor, and speedtorque curve C, which is obtained by applying a slightly decreased input potential to the motor.

When the motor is operating on curve B, its torque is sufficient to overcome the mass of the pulley and the weight, in which case the speed thereof causes the linear speed of the wire at the takeup reel to exceed the linear speed of the wire at the capstan. Consequently, since the wire is being taken up faster than it is being delivered, the loop formed by the pulley constantly decreases causing the pulley and weight to be raised to their uppermost switch-actuating positions. However, when the motor 33 is operating on the curve C, its torque is not sumcient to overcome the mass of the pulley and the weight, whereupon the speed thereof causes the linear speed of the wire 2| at the reel 3| to be less than the linear speed of the wire at the capstan. In this case the loop formed by the pulleys constantly increases allowing the pulley and weight to descend to their lowermost switch-actuating position. Since the motor 33 is arranged to develop parallel speed-torque curves for different input voltages, the curves B and C, being produced by different input potentials, are parallel to the ideal curve A throughout the operating range of the motor 33. Since the curves B and C are parallel to each other, the changeover from curve B to curve C and vice Versa produces a corresponding decrease or increase in the torque of the motor 33. This feature of the motor 33 provides a uniform rising and falling of the pulley 24 and the weight 34 between their switch-actuating limits and prevents any undue jerks on the wire 2| at the time of changeover from curve B to curve C or vice versa. Fig. 2 also illustrates that many parallel speedtorque curves may be obtained by varying the input potential to the motor. The selection of the ideal operating speed-torque curve for the motor 33, such as the curve A, depends upon the size of the mass of the weight 34 carried by the pulley 24. The weight 34 in turn is selected to exert a constant tension on the 'wire 2| commensurate with the size of the wire so that the wire will be wound tightly on the reel 3| without causing the wire to pull down in-between the convolutions of the previous layer of wire on the reel. Therefore, it is necessary to determine the ideal curve for any given operating condition of wire size and tension exerted by the Weight 34, such as curve A, and then adjust the taps of the autotransformer 5? so that the motor 33 will operate alternately on speed-torque curves which straddle the ideal curve, such as the speed-torque curves B and C (Fig. 2). The alternate operation of the motor 33 on the curves B and C provides an alternate rising and fallingor" the weight 34 between their switch-actuating limits, thereby maintaining the fixed tension on the wire 2| even though the torque of the motor is alternately varying between the selected high and low limits determined by the selected curves B and C.

The above-described apparatus operates as follows:

A suitable amount or" wire i is drawn from the supply reel 43 and threaded through the dies of the wire drawing machine it. The wire then is passed around the pulleys 22, 24 and 26 to form an adjustable loop and thence to the takeup reel 3|. The adjustable loop in the wire 2| is formed so that the weight and pulley supported by the loop assume a position midway of their uppermost and lowermost positions, whereby an intermediate length of wire 25 exists between the capstan E6 and the takeup reel 3|. The weight 34, having a known mass sufficient to exert the required tension on the wire '2 i to produce a tightly wound reel, is positioned so as to be carried by the pulley 23. Having determined the tension at which the wire is to operate, the proper taps of the transformer 51 are connected to the contactor so that the motor will operate either in the high torque curve B or the low torque curve C. With the weight and pulley in this position, the arms 35 and 33 are positioned so that they pivot downwardly and hold the arm 3! so that the arm .3 of the toggle switch 32 bridges the contacts 45 and 4'! of the switch 42. With the wire positioned in this manner, the means provided in the controller 53 for initiating the wire drawing operation is actuated by the operator of the machine.

Upon initiation of the wire drawing operation, the controller 53 simultaneously directs the threephase potential from a suitable supply (not shown) to the motor 28 and to the autotransformer 5?, and also energizes the magnetic clutch 60 so that the motor 23 is driving both the capstan l6 and the takeup reel 3|. At the same time, the coil 53 of the contactor 54 is energized by the position of the contact arm 43 of the switch 42, thereby positioning the contacts of the contactor 54 so that a selected voltage is applied to the input terminals of the motor 33 from the autotrans" former 51 causing the motor to operate on curve B. Due to the fact that the clutch 60 is energized, themctor 33 is not connected to the shaft 32 but is running, with no load applied thereto.

The wire drawing machine operates in this manner fora predetermined period of time regulated by the controller 5c, during which period the wire drawing machine is allowed to come up to full speed operation. Since the magnetic clutch is energized upon the starting of the wire drawing operation, the reel 3| and the capstan |5 are accelerated at the same rate of speed. During this accelerating period, the drive between the motor 20 and the shaft 32 is arranged to produce a peripheral speed of the winding diameter of the reel substantially equal to the peripheral speed of the last step of the capstan l6. Under these operating conditions the pulley 24 and the weight 34 carried thereby remain in their starting positions, and together exert a constant tension on the wire 2| being taken up by the reel 3|.

However, when the wire drawing machine l4 is brought up to full speed by the motor 20, it is necessary to vary the speed of the takeup reel 3| in order to compensate for the constantly increasing winding diameter of the reel, which causes the peripheral speed of the reel 3| to exceed that of the capstan l6. Therefore, as soon as the wire drawing machine is operating at full speed, the control apparatus 50 deenergizes the magnetic clutch 60, whereupon the motor 33, which is operating on curve B, takes over and drives the reel 3|.

The wire drawing operation continues in this manner, and as the motor is operating on curve B, its torque is sufficient to overcome the mass of the weight and the pulley. Eventually the speed of the wire 2| at the reel exceeds the speed of the wire at the capstan Hi. When this occurs, the reel 3| is taking up the wire 2|, passing through the adjustable loop formed'by the rollers 22, 24, and 26, at a rate faster than the wire 2| is being delivered by the capstan l6.

Since the rate of takeup of the wire 2| is greater than the rate of supply, the adjustable loop is contracted, causing the weight 34 and the pulley 24 to be slowly raised toward their uppermost switch-actuating positions. During the movement of the pulley 24 from its lowermost position to its uppermost position, the pulley 24 and the weight 34 carried thereby exert a constant, predetermined tension on the wire 2|, and this tension remains constant even though the torque of the motor 33 is such that the takeup speed of the wire is greater than the delivery speed of the wire.

Continued operation of the wire drawing machine |4 under these conditions will eventually contract the adjustable loop to a point where the weight and pulley will reach their uppermost switch-actuating positions. In so doing, the

pulley 24 engages the free end of the arm 36 and moves it upwardly causing the car 40 of the arm 31 to move downwardly and engage the arm 43 of the switch 42. Continued upward movement of the arm 36 eventually will cause the ear 40 to operate the arm 43 so that it bridges the contacts 44 and 45 of the toggle switch 42. When the arm 43 is operated in this manner, the coil 53 is deenergized and the coil 52 is energized causing the contacts of the magnetic contactor 54 to be arranged so as to connect a substantial portion of the autotransformer 51 in circuit with the motor 33. By connecting a greater portion of the autotransformer 5'! in the circuit to the motor 33, a selected lower voltage is applied across its input terminals, causing the motor 33 to operate on speed-torque curve C (Fig. 2). Since curve C is parallel to the selected speed-torque curve B, a corresponding reduction in torque and speed of the motor is effected by the application of reduced potential to the motor.

With the motor 33 operating on curve C, it: torque is not sufiicient to overcome the mass of the pulley and weight, whereupon the speed of the reel is reduced so that the speed of the wire at the reel 3| is less than the speed of the wire at the capstan. The wire 2| then is taken up by the reel 3| at a rate less than the rate at which the wire is being delivered to the adjustable loop by the capstan. Under these operating conditions, the loop slowly enlarges and the weight and pulley descend toward their lowermost switch-actuating positions. Throughout the entire downward travel of the pulley and the weight, they exert the same constant tension on the wire 2|, in spite of the fact that the takeup rate of the wire is now less than the delivery rate of the wire. In other words, the changeover in the operation of the motor 33 from curve B to curve C does not afiect the tension applied to the wire 2| by the weight and the pulley.

As the motor 33 continues to operate on curve C, the weight and pulley ultimately reach their lowermost switch-actuating positions and actuate the arm 35 downwardly. In so actuating the'arm 35, the trip arm 31 is raised so that the ear 40 thereof engages and actuates the arm 43 or the switch 42. Upon such actuation of the arm 43, coil 52 is deenergized, coil 53 is energized and shifts the contacts of the contactor 54 so that the autotransformer 51 delivers an input voltage to the motor 33 which causes it to again operate on curve B. The torque and, consequently, the speed of the motor 33 increases, where upon the speed of the wire at the takeup reel 3| is greater than the speed of the wire at the capstan l6.

Under this operating condition, the adjustable loop is again contracted and raises the pulley and weight to their upper switch-actuating position. In so doing, the pulley 24 engages the arm 35 and operates the arm 31 which actuates the switch arm 43 and causes the motor to again ope erate on reduced voltage and the corresponding speed-torque curve C. The operation of the takeup motor 33 continues to alternate back and forth between the upper and lower selected speed-torque curves B and C, respectively, until the takeup reel 3| is full, at which time the wire drawing operation is terminated. The full reel is removed from the shaft 32, an empty reel positioned thereon, and the wire drawing operation is resumed during which the above-described takeup operations are repeated.

It is believed to be apparent from the above described operation of the apparatus that as long as the weight 34 and the pulley 24 are free to travel between their switch-actuating limits their combined weight exerts a constant tension on the wire 2!. The feature of varying the torque of the motor between high and low limits selected in accordance with the wire size and tension to be exerted thereon permits the weight to rise and fall and maintain a constant tension on the wire throughout the takeup operation of the wire from an empty reel to a full reel. By maintaining constant tension on the wire during the takeup operation, a tightly wound reel is obtained, from which the wire may be freely unwound in subsequent processing operations of the wire.

While the above-described apparatus is particularly well adapted to maintain a constant tension on a wire being taken up from a wire drawing machine it may readily be used to maintain constant tension on filamentary strands emerging from various types of continuous strand processing apparatus such as twisting machines, textile insulating machines and continuous vulcanizing machines. Therefore, the scope of the invention is to be limited only by the scope of the appended claims.

What is claimed is:

1. The method of maintaining uniform ten= sion on a strand advancing from a constant speed strand-working apparatus to a strand takeup apparatus, which comprises maintaining a variable supply of strand between the strand-working apparatus and the takeup apparatus, applying a predetermined fixed tension on the portion of the strand in the variable supply, applying a torque to the strand takeup apparatus sufficient to reduce the variabl strand supply to a predetermined minimum limit against the action of the fixed tension on the strand, then applying a torque to the takeup apparatus of such value that the fixed tension on the strand overcomes said torque and increases the variable strand supply to a predetermined maximum limit, and alternately changing the torque applied to the takeup apparatus from one of said values to the other of said values to maintain the variable strand supply within said predetermined limits so that only the fixed tension is applied to the strand throughout the takeup operation from an empty reel to a full reel.

2. The method of maintaining uniform tension on a strand advancing from a constant speed strand-working apparatus to a strand takeup apparatus, which comprises forming a variable loop in the strand between the strand-working apparatus and the takeup apparatus, applying a predetermined fixed tension in the portion of the strand in the variable loop, and alternately taking up the strand with a force sufiicient to overcome the fixed tension on the strand and decrease the variable loop by a predetermined amount and taking up the strand with a force which is overcome by the fixed tension on the strand and increases the variable loop by a predetermined amount, whereby only the predetermined fixed tension is applied to the strand as the takeup operation proceeds from an empty reel to a full reel.

3. The method of maintaining uniform tension on a strand being advanced from a constant speed strand-Working apparatus to a strand takeup reel driven by a variable speed motor, which comprises forming a variable loop in the path of travel of the strand between the strandworking apparatus and takeup apparatus, supporting a movable weight in the loop to apply a predetermined fixed tension in the strand forming the variable loop, applying a potential to the motor of such value that the resulting motor torque is sufiicient to overcome the tension applied to the strand and contract the variable loop to a predetermined limit, then applying a potential to the motor of such value that the fixed tension applied to the strand overcomes the resulting motor torque and enlarges the variable loop to a predetermined maximum limit, and alternately changing the potential applied to the motor from one of said values to the other of said values to reciprocate the weight between said limits so that only the weight tensions the strand as the takeup of the strand proceeds from an empty reel to a full reel.

4. An apparatus for maintaining uniform tension on a strand advancing from a constant speed strand-working apparatus to a strand takeup apparatus, which comprises a takeup reel for receiving the strand from the strand workingapparatus, means for forming a variable loop in the path of travel of the strand between the strand- Working apparatus and the takeup reel, a weighted pulley riding freely in the adjustable loop for applying a predetermined fixed tension in the strand, means for driving the reel alternately with a force sufficient to overcome the weighted pulley and decrease the variable loop to a predetermined limit and with a force such that the weighted pulley overcomes-the force applied to the reel and increases the variable loop to a predetermined limit, and means operable by the weighted pulley for alternately changing the force applied to the reel from one of said 10 values to the other of said values to maintain the adjustable loop within said predetermined limits so that only the fixed tension applied to the strand by the weighted pulley acts on the strand as the takeup proceeds from an empty reel to afull reel.

5. An apparatus for maintaining uniform tension on a wire advancing from a capstan of a constant speed wire drawing machine, which comprises a reel for taking up the wire emerging from the wire drawing machine, a variable torque motor for driving the takeup reel, a system of pulleys including a freely movable pulley arranged to form a variable loop in the wire between the capstan and the takeup reel, said movable pulley being arranged to freely slide Vertically as the length of wire in the variable loop decreases or increase, a weight carried by the movable pulley for applying a predetermined fixed tension on the wire between the wire drawing machine and the takeup reel, means for varying the potential supplied to the motor, and means operable by said movable pulley for actuating the motor potential varying means so that the resulting motor torque maintains the adjustable loop within predetermined limits, said limits being selected so that only the weight applies tension on the strand throughout the takeup operation from an empty reel to a full reel.

6. An apparatus for maintaining uniform tension on a wire emerging from a capstan of a constant speed wire drawing machine, which comprises a takeup reel for taking up the wire emerging from the wire drawing machine, a

variable torque motor for driving the takeup reel, said motor having primary and secondary windings arranged to produce parallel speedtorque curves for different input voltages, a takeup reel driven by said motor, a system of pulleys including a freely movable pulley arranged to form a variable loop in the wire between the capstan and the takeup reel, said movable pulley being arranged to slide freely up and down as the length of the wire in the variable loop decreases or increases, a weight carried by the pulley and selected to apply a predetermined tension on the wire, means for varying the potential supplied to the primary terminals of the motor between a potential at which the motor decreases the variable loop to a predetermined minimum limit against the action of wei ht tensioning the strand and a potential at which the weight increases the variable loop to a predetermined maximum limit against the action of the motor, and a system of levers arranged to be actuated by the movable pulley at each of said limits for actuating the potential varying means so that the motor reeiprocates the Weight between said predetermined limits, whereby only the weight tensions the strand throughout the takeup of the strand from an empty reel to a full reel.

'7. An apparatus for maintaining uniform tension on a strand advancing from a constant speed strand-working apparatus to a strand takeup apparatus, which comprises a takeup reel for receiving the strand, means for maintaining a variable supply of strand between the strand-working apparatus and the takeup reel, means for applying a predetermined fixed tension on the strand in the said variable strand supply to the size of the strand, means for taking up the strand on the takeup reel alternately with a torque sufilcient to overcome the fixed tension on 11 the strand and decrease the variable strand supply to a predetermined limit and with a-torque which is overcome by the fixed tension on the strand so that the variable strand supply increases to a predetermined limit, and means responsive to the size of the variable strand supply for alternately varying the torque applied to the takeup reel to maintain the variable strand supply within said predetermined limits so that only the predetermined fixed tension acts on the strand throughout the takeup of the strand from an empty reel to a full reel.

8. The method of maintaining uniform tension on a strand advancing at a constant speed to strand takeup apparatus, which comprises forming a variable loop in the path of travel of the strand, supporting a freely movable weight in the loop to apply a predetermined fixed tension on the strand, taking up the strand with a force sufiicient to move the weight in one direction until it engages a predetermined limit, then taking up the strand with a force sufiicient to move the weight in the opposite direction until it engages a second limit, and alternately changing the takeup force applied to the strand from one of said values to the other of said values so that only the weight tensions the strand as it is taken up by the takeup apparatus.

9. An apparatus for'maintaining uniform tension on a strand advancing at constant speed to strand takeup apparatus, which comprises a system of pulleys including a freely 'movable pulley for forming a variable loop in the strand advancing to the takeup apparatus, a weight supported by the pulley for applying a predetermined fixed tension on the strand, adjustable means for taking up the strand with a force sufficient to move the pulley and weight in one direction and reduce the variable loop, means engaged by the pulley when the loop decreases to a predetermined limit for changing the force applied to the takeup means to such a value that the pulley and weight move in an opposite direction and increase the variable loop, and means engaged by the pulley when the loop increases to a predetermined limit for changing the takeup force so that the pulley and weight move in the first-mentioned direction, whereby the Weight maintains uniform tension on the strand throughout the takeup operation from an empty reel to a full reel.

CARL O. I-IAASE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

